It is generally known to use inkjet printers to print on paper-based products. The inkjet printer produces ink drops that are deposited onto the paper product to produce the finished printed product. A printhead including at least one ink cartridge containing nozzles producing the ink drops. The ink cartridge containing nozzles is moved repeatedly across the width of the paper. At each of a designated number of increments of this movement across the paper, each of the nozzles is caused either to eject ink, or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the paper can print a swath approximately as wide as the number of nozzles arranged in a column on the ink cartridge multiplied by the distance between nozzle centers. After each such completed movement or swath, the paper is advanced forward by approximately the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of signals output by the controller, the desired print is obtained on the paper. In order to obtain multicolored printing, a plurality of ink-jet cartridges, each having a chamber holding a different color of ink from the other cartridges, may be supported on the printhead.
One problem associated with inkjet printers is that water-based inks have a tendency to produce prints of a less than desirable quality. Typically, ink-jet printers are not able to print high density plots on paper-based media without suffering two major drawbacks: the saturated media is transformed into an unacceptably wavy or cockled sheet; and adjacent colors tend to run or bleed into one another. When the water-based ink is deposited on paper-based media, it absorbs into the cellulose fibers and causes the fibers to swell. As the cellulose fibers swell, they generate localized expansions that cause the paper to deform uncontrollably in these regions. This phenomenon is called paper cockle. This can cause a degradation of print quality due to uncontrolled pen-to-paper spacing, and can also cause the printed output to have a low quality appearance due to the wrinkled media.
Paper cockle may include lateral deformation. Lateral deformation is especially troublesome when printing on paper-based media that is printed in a horizontal plane and thereafter transported in a vertical plane. The lateral deformation is not instantaneous, because the water content takes some time to be absorbed into the media. The absorbing process takes place while the media travels from the horizontal printing plane and continues while the media travels in the vertical plane. The deformation makes the paper grow, and it grows with time, which means that the bottom part of the media is wider than the top part of the media. Therefore, the lateral expansion produces webs that are trapezoidal in shape as opposed to a normal rectangular shape. The paper-based web may sag or “smile” as it moves downwards, making it difficult to carry out further media processing. This problem occurs in inkjet printing machines, such as plotters, because plotters typically transport paper-based webs from a horizontal printing plane to a vertical exit plane.
The FIGS. 1A and 1B show an exemplary illustration of an inkjet printer 10 that may experience lateral expansion and paper cockle in general. The printer 10 may be a web fed inkjet printer 10 such as a plotter on a stand with legs 12. FIG. 1B is a cross sectional view and it shows a supply roll 20 on which is wound a paper-based web 11. The web is transported to the printhead 30 where it is printed upon while in a horizontal orientation. From the printhead, the web 11 is then transported in a vertical orientation. As illustrated in FIG. 1B, the web 11 falls out of the printer 10 through an exit 40 while maintaining the vertical orientation.
Prior art solutions to media deformation include the use of media deflectors as disclosed in U.S. Pat. No. 5,951,181. The deflectors taught in '181 are not heated. As result, the deflectors do not effectively prevent media expansion.
The prior art also discloses the use of heating elements positioned downstream of the printing area. These heating elements usually include a line of fans blowing warm air onto the media surface. Typically, these devices dry the ink on the media surface, so that media can be retrieved or rolled onto a take-up reel at a more efficient rate. However, these devices are not very efficient for controlling media deformations caused by ink expanding the paper fiber because they are not efficient at drying ink that is absorbed into the cellulose fibers.